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Mortality of brook trout Salvelinus fontinalis and water chemistry were characterized in 6 headwater streams in the western Adirondacks of New York during spring 2015, 2016, and 2017 and compared with results from analogous tests done between 1980 and 2003 in many of the same streams, to assess temporal changes in toxicity and inorganic monomeric aluminum (Ali) concentrations, and the role of Ali exposure duration on brook trout survival. The Ali concentrations of 2 and 4 µmol L–1 corresponded to low‐to‐moderate and high mortality thresholds, but prolonged exposure to ≥1 µmol Ali L–1 also produced mortality. The variability, mean, and highest Ali concentrations in Buck Creek year round, and in several other streams during spring, have decreased significantly over the past 3 decades. Logistic models indicate that Ali surpassed highly toxic concentrations in Buck Creek for 3 to 4 mo annually during 2001 to 2003 and for 2 to 3 wk annually during 2015 to 2017. The loss of extremely high Ali episodes indicates that toxicity has declined markedly between the 1989 to 1990, 2001 to 2003, and 2015 to 2017 test periods, yet Ali concentrations can still cause moderate‐to‐high and complete (100%) mortality. The logistic models illustrate how mortality of brook trout in several Adirondack streams likely decreased in response to the 1990 Amendments to the United States' Clean Air Act (which decreased acidity, Ali concentrations, and duration of toxic episodes) and offer a means to predict how changes in US regulations that limit emissions of NOx and SOx (and N and S deposition loads) could affect fish survival and stream ecosystems in this region and across the Northeast. Environ Toxicol Chem 2020;39:623–636. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Context: Preservation of genetic diversity is a commonly cited, yet under-evaluated aspect of species conservation plans. Understanding the influence of human-mediated translocations and habitat constraints on landscape patterns of genetic structure in threatened fish species is essential to maintaining biodiversity and adaptive potential. Objectives: We evaluated the degree of influence from supplemental stocking, assessed the spatial population genetic structure, and examined the potential relationship between hybridization and ecology for Brook Trout (Salvelinus fontinalis) in the Black River watershed in New York State, USA. Methods: We used 13 microsatellite loci from over 450 fish at 18 sampling locations to map genetic structure and diversity, estimate the level of influence from stocked conspecifics, and model the relationship between hybridization and ecological characteristics. Results: We found widespread genetic introgression attributable to state-based stocking activities and a pattern of hierarchical genetic diversity across the landscape, which has additionally been influenced by geography. Site-specific fish assemblage variables appear to be unrelated to introgressive hybridization from stocked conspecifics, and only one hydrochemical variable, SO42−, exhibited strong explanatory power in predicting hybridization between wild and supplemented fish. A single locality exhibited genetic structure consistent with no history of introgression potentially associated with differences in elevation, and thus contributed disproportionately to the level of genetic diversity observed across the landscape. Conclusions: When examining genetic structure in fluvial riverine networks, it is important to consider the combined and interacting effects of both hybridization and habitat, which may result in augmented genetic structure not predictable from any single factor. [ABSTRACT FROM AUTHOR]

Surface waters across much of New York's Adirondack Mountains were acidified in the late 20th century but began to recover following the 1990 amendments to the Clean Air Act. Little data, however, are available to characterize biological impacts and predict recovery of fish assemblages in streams of the region. Quantitative fish and chemistry surveys were completed in 47 headwater streams during summer 2014–2016 to develop logistic (probabilistic) models that characterize the status of contemporary fish assemblages and predict how different nitrogen (N) and sulfur (S) deposition loads may affect future fish assemblages. Models for inorganic monomeric aluminum (Ali) and richness ≥1 species and for acid neutralizing capacity (ANC) and total density >400 fish/0.1 ha, total biomass >1500 g/0.1 ha, brook trout (Salvelinus fontinalis) density >0 or >200 fish/0.1 ha, and brook trout biomass >1000 g/0.1 ha were suitable for evaluating community and population responses to changes in acid–base chemistry. Anticipated changes in national (US) secondary standards for atmospheric emissions of nitrogen oxides (NOx) and sulfur oxides (SOx) to achieve target N and S deposition loads will alter acid–base chemistry and the probabilities for observing various levels of fish metrics in streams across the region and elsewhere. [ABSTRACT FROM AUTHOR]

Water temperature is a key component of aquatic ecosystems because it plays a pivotal role in determining the suitability of stream and river habitat to most freshwater fish species. Continuous temperature loggers and airborne thermal infrared (TIR) remote sensing were used to assess temporal and spatial temperature patterns on the Upper Schoharie Creek and West Kill in the Catskill Mountains, New York, USA. Specific objectives were to characterize (1) contemporary thermal conditions, (2) temporal and spatial variations in stressful water temperatures, and (3) the availability of thermal refuges. In-stream loggers collected data from October 2010 to October 2012 and showed summer water temperatures exceeded the 1-day and 7-day thermal tolerance limits for trout survival at five of the seven study sites during both summers. Results of the 7 August 2012 TIR indicated there was little thermal refuge at the time of the flight. About 690,170 m2of water surface area were mapped on the Upper Schoharie, yet only 0.009% (59 m2) was more than 1.0 °C below the median water surface temperature (BMT) at the thalweg and no areas were more than 2.0 °C BMT. On the West Kill, 79,098 m2were mapped and 0.085% (67 m2) and 0.018% (14 m2) were BMT by 1 and 2 °C, respectively. These results indicate that summer temperatures in the majority of the study area are stressful for trout and may adversely affect growth and survival. Validation studies are needed to confirm the expectation that resident trout are in poor condition or absent from the downstream portion of the study area during warm-water periods. [ABSTRACT FROM AUTHOR]